Method and apparatus for the highspeed carbonisation of solid fuels of small particle size,such as coal



Oct. 20,1970 P. LEDENT 3,535,209

METHOD AND APPARATUS FOR THE HIGPFSPEED CARBONISATION OF SOLID FUELS OF SMALL PARTICLE SIZE, SUCH AS COAL Filed July 1. 1968 INVENTOR IA-19,9! 150:;-

MA Q ATTORNEY United States Patent Int. Cl. mob 1/02, 47/24 US. Cl. 20127 6 Claims ABSTRACT OF THE DISCLOSURE Process for the carbonisation of a particulate solid fuel, which comprises: in a first stage subjecting said solid fuel to preliminary carbonisation at a temperature of from 500 to 600 C. in a fluidised bed; and, in a second stage, subjecting said carbonised solid fuel to further carbonisation at a temperature of from 700 to 900 C. in a vertical stack by entraining said carbonised solid fuel in an inert gas, to produce a hot semi-coke.

The present invention concerns improvements in or relating to method and apparatus for the high-speed carbonisation of solid fuels of small particle size, such as coal.

The method and apparatus of the present invention are designed to carbonise coal or other solid fuels of small particle size (in generaly up to mm.) up to a final temperature of the order of 700 to 900 C., in order to convert it to a semi-coke suitable, for example, as a thinner in coke paste or as a basic material for the manufacture of moulded coke.

It is known to prepare semi-cokes of this kind by fluidised bed techniques of carbonisation or by stack gas techniques. However, each of these procedures has its drawbacks.

The technique of carbonisation by injecting air into a fluidised bed of the solid fuel results in a partial gasification. of the fuel with a resulting substantial decrease in the output of semi-coke and a high production of lowquality gas and tar by-products, the purification and use of which are extremely diflicult.

carbonisation by entraining the solid fuel in a stack produces extremely rapid heating with the result that the end-product semi-coke is highly expended.

The method and apparatus of the present invention overcome these difliculties and achieve three objectives.

(1) The avoidance of too rapid heating in the transitional zone within which the coal changes state, which prevents the porduction of an excessively expanded semicoke;

(2) The avoidance of any gasification of the semicoke, which results in a high output of solid product;

(3) The avoidance of the production of tar-bearing by-products which are diflicult to purify and use.

In order to achieve these objectives, the process in accordance with the invention combines preliminary carbonisation in fluidised bed fashion at a temperature in the order of 500 to 600 C., with carbonisation by entrainment through a vertical stack, at a final temperature between 700 and 900 C.

The heat required to raise the temperature of the semicoke in the stack may be supplied by the hot gases deriving from the combustion of all or part of the tarbearing gases resulting from fluidised bed process; the

eat required to raise the temperature of the fluidised bed, which forms the preliminary carbonisation stage, is

supplied by recycling part of the hot semi-coke coming from the stack.

The invention is now further illustrated with reference to the accompanying drawings, in which:

FIG. 1 is an elevational section of apparatus according to the invention and FIG. 2 a section on the line II-II of FIG. 1.

The preliminary carbonisation chamber 1, the base of which is a porous wall or a grid 2 through which an inert gas is blown at a speed sufficient to keep the fine particles of which the bed 3 is made up in a fluidised condition, is supplied with recycled hot semi-coke through an orifice 4 located above the surface of the fluidised bed, and with crude solid fuel from a rotary distributor 5 which distributes the fuel over the surface of the fluidised bed.

This preliminary carbonisation chamber 1 is associated with a pneumatic heating and stack (elevation) device. The stack device comprises: a closed chamber 6 whose walls are lined with refractory material and which has a porous base, within which the particulate fuel to be processed is maintained in a fluidised condition by the introduction of an inert gas through the porous base; a vertical stack 7 which passes through the upper wall of the chamber 6 and extends into the said chamber down to the level of the aforementioned fluidised bed; and a burner 8 located tangentially within the vertical wall of the said chamber 6 and above the level of the fluidised bed.

The preliminary carbonisation chamber 1 communicates with chamber 6 via two orifices: a lower orifice 9, situated below the level of the fluidised bed through which passes the solid materials, and an upper orifice 10, through which the gas resulting from the fluidisation process and the distillation products (gas and tar) enamating from chamber 1, are injected tangentially into the chamber 6 at a level above the level of the fluidised bed.

The preheating of the system is eflected by the hot gases coming through the burner 8.

Once the said preheating has been effected, all the heat required for the operation of the installation derives from the combustion of the distillation products from the chamber 1. This combustion is carried out in the upper part of the chamber 6, which has the function of a cyclone, the air charge required for combustion being introduced by the burner 8 or possibly through another orifice such as the orifice 11, located tangentially to the chamber and above the level of the fluidised bed. The neutral gas produced in chamber 6 by combustion of the tars and the distillation gases coming from the chamber 1, plus the solid fuel fed into the fluidised bed through the orifice 9, rise together through the stack 7 which causes heat exchange between the hot gases and the solid materials.

In high-capacity installations, a second stack tube 12 of smaller diameter and sealed at least at the lower end may be provided inside the stack 7, the annular space exclusively between the two can be used for the circulation of the gases and the solids.

At the top of the stack, the gases and the solids are separated in the chamber 13. The hot semi-coke is gravity evacuated into a porous-base chamber 14 communicating with the preliminary carbonisation chamber '1 through the orifice 4, said chamber 14 containing a weir 15 across which the excess semi-coke is discharged after passing through a fluidised siphon.

The hot gases, at a temperature of the order of 700 to 900 C. and enriched with the distillation gases liberated from the semi-coke during its passage through the stack 7, are ridded of their solids content in the cyclone 16 after which they are directed into a chamber 17 where combustion of the residual gases takes place.

The flow of high temperature gases thus obtained may be used to produce steam in the waste-heat boiler 18 and, possibly, may also be used for other purposes such as pre-heating combustion air, re-heating the natural gases used for the fluidisation technique, or for drying solid fuel prior to its introduction into the carbonising installation.

In a variant embodiment which has not been illustrated, the direct communication 10 designed to carry the tar-bearing gases, can be discarded and replaced by an external link comprising a purifying system in which the gsa has the solids removed from it and the tars condensed, the purified gas being reinjected wholly or partly into the chamber 6 through the medium of the burner 11.

I claim:

1. A process for the carbonization of a particulate solid fuel, which comprises: in a first stage subjecting said solid fuel to preliminary carbonization at a temperature of from 500 to 600 C. in a fluidised bed; and, in a second stage, subjecting said carbonized solid fuel to further carbonization at a temperature of from 700 to 900 C. in a vertical stack by entraining said carbonized solid fuel in an inert gas, to produce a hot semi-coke; wherein the heat necessary for the preliminary carbonization in said first stage is provided by recycling part of said hotcoke, and in which the heat necessary for said further carbonization in said second stage is supplied by the hot gases resulting from combustion of all or part of the tar gases and vapours liberated during the said first stage.

2. Apparatus for carbonization of a particulate fuel comprising a fluidised bed, at least two closed porousbased vessels having means for blowing an inert gas through said porous based vessels, means for introducing particulate solid fuel into one of said vessels, a vertical stack passing through the top wall of the other vessel and extending inside said other vessel to the desired level of the fluidized bed, said two vessels communciating with one another through a lower orifice situated below the level of the fluidized bed, and through an upper orifice situated above the level of said fluidised bed and opening tangentially into said other vessel, and means at the upper end of said stack for separating the solid fuel from the inert gas.

3. Apparatus according to claim 2, in which said other vessel has the form of a vertical cylinder lined internally with refactory material and containing a tangentially arranged pre-heating burner.

4. Apparatus according to claim 2, wherein means are provided for returning at least part of the hot semi-coke issuing from said vertical stack to said first vessel.

5. Apparatus according to claim 4, wherein the hot semi-coke coming from the stack is gravity returned to a porous-based vessel in which it is fluidised by the introduction of steam or neutral bases, which vessel communicates through an orifice situated above the level of the fluidised bed, with the vessel into which the crude coal is fed.

6. Apparatus according to claim 5, wherein means are provided to burn the residual gases contained in the gas mixture leaving the stack, the resultant head being utilised in a waste-heat boiler, in an even for drying the crude fuel or in air or gas heaters.

References Cited UNITED STATES PATENTS 2,582,712 1/1952 Howard 20l3l XR 3,043,752 7/1962 Foch 20l44 XR 3,140,240 7/1964 Fowler 201-31 XR 3,412,013 11/1968 Bowles 23-288.3

WILBUR L. BASCOMB, 111., Primary Examiner D. EDWARDS, Assistant Examiner U.S. Cl. X.R. 

